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How to create a heart shape using CSS?

I've found the following CSS in one of the answers here on SO and I was wondering why does it create the desired heart shape:

#heart { 
    position: relative; 
    width: 100px; 
    height: 90px; 
} 

#heart:before, #heart:after { 
    position: absolute; 
    content: ""; 
    left: 50px; 
    top: 0; 
    width: 50px; 
    height: 80px; 
    background: red; 
    border-radius: 50px 50px 0 0; 
    transform: rotate(-45deg); 
    transform-origin: 0 100%; 
} 

#heart:after { 
    left: 0; 
    transform: rotate(45deg); 
    transform-origin :100% 100%; 
}
<div id="heart"></div>

Please can someone explain?

Solution

  • CSS3 Mon Amour - A 4 Step Love Afair

    There are a few steps for creating heart shape using CSS3:

    1. Create a block-level element such as a <div> in your DOM and assign it with id="heart" and apply CSS:

      #heart {
     position:relative; 
     width:100px; 
     height:90px;
     margin-top:10px; /* leave some space above */
}

    2. Now using pseudo-element #heart:before we create a red box with one rounded edge like this:

      #heart:before {
    position: absolute; 
    content: ""; 
    left: 50px; 
    top: 0; 
    width: 52px; 
    height: 80px; 
    background: red; /* assign a nice red color */
    border-radius: 50px 50px 0 0; /* make the top edge round */ 
}

      Your heart should now look like this:

      enter image description here

    3. Let us assign a little rotation to that by adding:

      #heart:before {
    -webkit-transform: rotate(-45deg); /* 45 degrees rotation counter clockwise */
       -moz-transform: rotate(-45deg); 
        -ms-transform: rotate(-45deg); 
         -o-transform: rotate(-45deg); 
            transform: rotate(-45deg); 
    -webkit-transform-origin: 0 100%; /* Rotate it around the bottom-left corner */
       -moz-transform-origin: 0 100%; 
        -ms-transform-origin: 0 100%; 
         -o-transform-origin: 0 100%; 
            transform-origin: 0 100%;
}

      And we now get:

      enter image description here

      Already starting to come together :).

    4. Now for the right part we basically need the same shape only rotated 45 degrees clockwise instead of counter clockwise. To avoid code duplication we attach the css of #heart:before also to #heart:after, and then apply the change in position and in angle:

      #heart:after { 
    left: 0; /* placing the right part properly */
    -webkit-transform: rotate(45deg); /* rotating 45 degrees clockwise */
       -moz-transform: rotate(45deg); 
        -ms-transform: rotate(45deg); 
         -o-transform: rotate(45deg); 
            transform: rotate(45deg); 
    -webkit-transform-origin: 100% 100%; /* rotation is around bottom-right corner this time */
       -moz-transform-origin: 100% 100%; 
        -ms-transform-origin: 100% 100%; 
         -o-transform-origin: 100% 100%; 
            transform-origin :100% 100%; 
}

      And voilà! a complete heart shaped <div>:

      enter image description here

    Snippet without any prefix:

    #heart {
  position: relative;
  width: 100px;
  height: 90px;
  margin-top: 10px;
}

#heart::before, #heart::after {
  content: "";
  position: absolute;
  top: 0;
  width: 52px;
  height: 80px;
  border-radius: 50px 50px 0 0;
  background: red;
}

#heart::before {
  left: 50px;
  transform: rotate(-45deg);
  transform-origin: 0 100%;
}

#heart::after {
  left: 0;
  transform: rotate(45deg);
  transform-origin: 100% 100%;
}
    <div id="heart"></div>